Lesson-Popliteal

36 – Enhanced visibility after injection

After injection of the local anaesthetic, the sciatic nerve is more easily visualised due to the contrast between the bright (hyperechoic) sciatic nerve and the background of the black (anechoic) local anaesthetic

Click on the VIDEO CLIP button to view the video

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The visibility of the peroneal nerve (P) and the tibial nerve (T) is enhanced after perineural injection of a black halo

37 – Reduced nerve visibility in obese patients

The visibility of the sciatic nerve and its branches are often reduced in the very obese patients

In obese patients it may be required to use a curved array transducer in order to perform a popliteal sciatic nerve block

However, the sciatic branches – the tibial nerve and the common peroneal nerve – are often sonographically visible near the popliteal crease, where they are usually superficially located. Even in obese patients

Click on the VIDEO CLIP button to view the video

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The video shows blurred visibility of the sciatic nerve branches in an obese patient. A curved array transducer is employed to allow deeper depth of penetration of the ultrasound beam
BFM = biceps femoris muscle; PN = common peroneal nerve; TN = tibial nerve; PA = popliteal artery

32 – Avoid intraneural injection of local anaesthetic

It is important not to penetrate the target nerves with the block needle and especially not to inject local anaesthetic intraneurally

Insert the needle tangentially to the branches of the sciatic nerve in the popliteal fossa

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The needle tip is placed intraneurally and needs to be relocated before injection of local anesthetic

Needle is indicated by arrow head

33 – You can touch the nerve but don’t pierce it

You can touch the nerve with the needle, but you should not pierce it

And especially you should not inject local anaesthetic intraneurally

Click on the VIDEO CLIP button to view the video

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The video shows how the tibial nerve (TN) can be touched by the needle as long as it does not pierce the nerve

34 – Blocking the sciatic nerve proximal to the bifurcation

It is also possible to move the probe proximal to the bifurcation of the sciatic nerve and block the nerve guided by ultrasound at this level

Click on the VIDEO CLIP button to view the video

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The video shows the sciatic nerve (S) in cross section just proximal to its bifurcation in the popliteal fossa. Local anesthesic (LA) is injected perineurally
PN = peroneal nerve; TN = tibial nerve

35 – The endpoint of injection

The endpoint of injection is complete perineural spread of local anaesthetic

Click on the VIDEO CLIP button to view the video

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This video clip demonstrates complete perineural spread of local anaesthetic around the common peroneal nerve (P) and the tibial nerve (T) distal to the branching of the sciatic nerve in the popliteal fossa

30 – Complete perineural spread of local anaesthetic by relocating the needle tip

The endpoint of ultrasound guided peripheral nerve blockade is complete perineural spread of local anaesthetic

This can be obtained by repositioing the tip of the needle during injection

Click on the VIDEO CLIP button to view the video

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The video shows complete perineural injection of local anaesthetic around the tibial nerve by relocating the needle tip

31 – Relocating the needle tip

The in-plane approach to block the two branches of the sciatic nerve – the tibial nerve and the peroneal nerve – allows real-time visualisation of the needle tip, the target nerves and the perineural spread of the local anesthetic

It also gives the opportunity to relocate the needle tip, if the spread is not perfect

The real time ultrasound imaging also makes it possible to avoid piercing the peroneal nerve, when the needle is advanced towards the tibial nerve

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The image simultaneously displays the target nerve (tibial nerve = T), the needle and needle tip and the peroneal nerve (P) allowing the operator to avoid piercing it when advancing the needle towards the tibial nerve

22 – Non-sciatic innervation of the leg, ankle and foot

The sciatic nerve branches (the tibial nerve and the common peroneal nerve) innervate the entire leg, ankle and foot

The only exception is the saphenous nerve territory and a strip of skin distal to the popliteal fossa which is innervated by the posterior femoral cutaneous nerve

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The green area is the cutaneous innervation area of the saphenous nerve. The saphenous nerve innervates the skin on the medial side of the leg and foot. The saphenous nerve is the major branch from the femoral nerve (see the femoral nerve).

23 – Non-sciatic innervation of the leg

The posterior cutaneous nerve of thigh (also known as the posterior femoral cutaneous nerve) is a branch of the sacral nerve plexus and leaves the pelvic cavity through the greater sciatic foramen

It supplies a vertical strip of skin extending from the distal gluteal region down to mid-calf level

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The green colour depicts the posterior femoral nerve territory below the popliteal crease